Such an assembly is known in which the water box and the expansion chamber are disposed generally vertically with the upper part of the expansion chamber being provided with a liquid filler orifice suitable for receiving a stopper that includes a set of over pressure and under pressure release valves. The cross section of the expansion chamber tapers going down from the top in order to facilitate with drawing a molding core, andd the said communication orifice is at or near the bottom of the expansion chamber.
This known arrangement suffers from various drawbacks. Firstly, the stopper for closing the top of the expansion chamber must either have at least the same area as the largest cross section of the expansion chamber, which means that outsize stoppers have to be used with expansion chambers of ordinary size, or else some kind of funnel shaped cover must be fitted to the top of the expansion chamber, or else the expansion chamber must be re-designed to be of smaller cross section than usual in order to receive a normally sized stopper. Secondly, it is inconvenient for the small end of the expansion chamber's taper to be the end near to its communication orifice with the water box, since under these circumstances, a shortage of water in the radiator then causes the water level to drop more quickly in said end of the expansion chamber, and it may drop right down to the said communication orifice.
Further, the relatively small cross section at the bottom end of the expansion chamber causes liquid to circulate more quickly in this zone, which leads to there being an increased danger of air bubbles going into the radiator via the communication orifice, and hence to poorly de-gassed liquid circulating therein.
Preferred embodiments of the present invention reduce these drawbacks.